If an award were ever given to the person in history who was most dedicated to the pursuit of absolute precision, the German astronomer Johannes Kepler (1571–1630) might well be the recipient, notes Stephen Hawking in his introduction to this edition of Kepler's Harmonies of the World. And like Copernicus, Kepler was a deeply religious man, whose continual studies of universal properties were an attempt to understand God's plan. Kepler's three laws of planetary motion are still taught today, and it was his Third Law—not an apple—that led Isaac Newton to discover the law of gravitation. This is one of a series of original founding texts by the giants of modern physics and astronomy, with Hawking's introductory commentary on their life and work.